Luke Lonergan wrote:
On 11/7/07 10:21 PM, "Gregory Stark" <stark@xxxxxxxxxxxxxxxx> wrote:
part=# explain SELECT * FROM n_traf ORDER BY date_time LIMIT 1;
QUERY PLAN
-----------------------------------------------------------------------------
--------------------------------------------------------------------
Limit (cost=198367.14..198367.15 rows=1 width=20)
-> Sort (cost=198367.14..200870.92 rows=1001510 width=20)
Sort Key: public.n_traf.date_time
-> Result (cost=0.00..57464.92 rows=1001510 width=20)
-> Append (cost=0.00..57464.92 rows=1001510 width=20)
-> Index Scan using n_traf_date_time_login_id on n_traf
(cost=0.00..66.90 rows=1510 width=20)
That looks suspicious. There's likely no good reason to be using the index
scan unless it avoids the sort node above the Append node. That's what I hope
to do by having the Append executor code do what's necessary to maintain the
order.
Yah - the way it works in GPDB is that you get a non-sorting plan with an
index scan below the parent - that was the point of the fix. Hmm.
Unfortunately our plan in GPDB looks exactly the same in this case - so
we have a bit of work to do as well! Initially I wondered if I have got
something wrong in the patch... and checked on GPDB - only to see the
same behaviour! (see prev comment about LIMIT).
Cheers
Mark
---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend
